KEF LS50 Meta Review (Speaker)

[ctrl]

I think that you missunderstood me - the bass unit is modulating the tweeter depending on cone placement.
In Erins measurement theres only the tweeter sounding in this particular measurement. On the bass unit he has a battery, no amplifier.
And the difference in frequency response is big for the tweeter depending on where the bass cone is.

No I didn't misunderstand you. I explained that by the time the woofer is moving that much, the distortion it generates is much of a concern than whatever tweeter is doing.

Theoretically, the effect of "directivity modulation" of the tweeter, by excursion of the woofer, already occurs when the woofer still shows linear excursion.

In a general thread about coaxial speakers I had once simulated this for a driver with 10cm cone with +-3mm excursion.
The woofer of the KEF LS50 should also have at least (rather more) +-3mm linear excursion.

I have summarized the results as an animation, so one can better see the effects of the different cone positions:
1. Cross-sectional sketch, tweeter (blue) with different cone positions
2. Normalized frequency response
3. Normalized sonogram

At +-3mm excursion of the woofer, the "directivity modulation" only has a noticeable effect on the radiation of the tweeter at frequencies above 6kHz.
The question now is whether this already leads to perceptible psychoacoustic effects. The states shown in the animation are not stationary, but change with the frequency of the low-frequency reproduction.

 

[amirm]

At +-3mm excursion of the woofer, the "directivity modulation" only has a noticeable effect on the radiation of the tweeter at frequencies above 6kHz.
The question now is whether this already leads to perceptible psychoacoustic effects.

Thanks for the simulation. As I noted in the review, the only distortion I could hear when the volume was turned up was that of bass.

 

[ctrl]

Thanks for the simulation. As I noted in the review, the only distortion I could hear when the volume was turned up was that of bass.

I wouldn't expect a direct coloration of the sound at +-3mm excursion either, since the "directivity modulation" effects only occur above 6kHz.

But perhaps some listeners find coaxial speakers at these cone excursions (+-3mm) or above "exhausting" during extended listening, as the brain probably has to work harder to compensate for the "directivity modulation".

However, it is also clear that with a subwoofer (in the case of the LS50) or even more so when used as a midrange driver (in the higher-quality models from KEF), the "directivity modulation" of the tweeter is minimized and should (almost) no longer play a role.

 

[SS55]

Yes, good point. I would confirm whether the first two filters make an improvement or not by listening/measurements. As you said, depends on your room, how close you have the speakers to the front wall and of course your sub crossover freq.

That's a nice a nice opportunity and $500 extra sounds like a better deal (I believe you mentioned 800 previously). See @phoenixdogfan comment #279

Ah yes my bad, it's $800 extra for meta, since I got the original LS50 at a much lower price there is no discount on the meta and R3.

I am currently playing with the eq as mentioned and the new meta will arrive tomorrow so it's a good opportunity to test original (with/without eq) vs meta. Thanks for the suggestion.

 

[JohnYang1997]

I wouldn't expect a direct coloration of the sound at +-3mm excursion either, since the "directivity modulation" effects only occur above 6kHz.

But perhaps some listeners find coaxial speakers at these cone excursions (+-3mm) or above "exhausting" during extended listening, as the brain probably has to work harder to compensate for the "directivity modulation".

However, it is also clear that with a subwoofer (in the case of the LS50) or even more so when used as a midrange driver (in the higher-quality models from KEF), the "directivity modulation" of the tweeter is minimized and should (almost) no longer play a role.

I think it directly causes distortion and it will be measurable. In the form of IMD should be very easy to measure.
However it only happens at higher level which for such driver is not good. At lower level the effect should be very small. One should consider a dedicated sub with this.

 

[eddantes]

Theoretically, the effect of "directivity modulation" of the tweeter, by excursion of the woofer, already occurs when the woofer still shows linear excursion.

In a general thread about coaxial speakers I had once simulated this for a driver with 10cm cone with +-3mm excursion.
The woofer of the KEF LS50 should also have at least (rather more) +-3mm linear excursion.

I have summarized the results as an animation, so one can better see the effects of the different cone positions:
1. Cross-sectional sketch, tweeter (blue) with different cone positions
2. Normalized frequency response
3. Normalized sonogram

View attachment 146490

At +-3mm excursion of the woofer, the "directivity modulation" only has a noticeable effect on the radiation of the tweeter at frequencies above 6kHz.
The question now is whether this already leads to perceptible psychoacoustic effects. The states shown in the animation are not stationary, but change with the frequency of the low-frequency reproduction.

Very interesting animation! I'm curious - will "horn" (tulip?) mounted coaxials like Tannoys exhibit less of this? And finally - is this even audible?

 

[nothingman]

This is a nice animation but at least in terms of the Metas and I think KEF’s UniQ generally, it doesn’t really give enough credit to how much of the waveguide is static. This shows the midwoofer’s “pivot point” (for lack of good jargon) sort of midway up the tweeter dome, while the UniQ waveguide extends much higher, beyond the top of the dome. Surely this helps the effect shown in the animation and predicted response?

 

[SS55]

This is a nice animation but at least in terms of the Metas and I think KEF’s UniQ generally, it doesn’t really give enough credit to how much of the waveguide is static. This shows the midwoofer’s “pivot point” (for lack of good jargon) sort of midway up the tweeter dome, while the UniQ waveguide extends much higher, beyond the top of the dome. Surely this helps the effect shown in the animation and predicted response?

Good point, The tangerine waveguide is static and taller than the tweeter.

The surface area of the midrange cone can be compared to a conventional 4 inch driver as the tangerine waveguide takes up a lot of space for it to be called a true 5.25 inch driver. Keeping that in mind the low end performance is impressive. Not just the LS-50 but also the LSX which has -3db at 70hz according to spin data and it managed to impress @amirm

 

[aarons915]

Receivers with 12dB HP filtering for the main speaker, is made for closed box main loudspeakers that naturaly rolls of 12/dB oct at their resonance frequency. 12 dB HP plus 12 dB natural roll off = 24 dB. It can then sum correctly to the subwoofers 24dB/oct LP filter. Meaning that in most cases a crossover about 80 Hz is the best if you use a AVR crossover. Only very small main speakers have their resonance frequency at 150 Hz.

Thats how the THX 24/12 filtering works.

Thanks I think most of us know how the THX spec works, which is not really relevant to what we we're talking about. The point of higher crossover points than 80 is to transfer more distortion and reduce cone excursion of smaller speakers. The LS50's biggest weakness is bass response and bass distortion, so crossing them in the 100-120Hz range allows them to play loud enough for most people with much less distortion. Room EQ or manual EQ with measurement can be used to ensure the mains and subs sum correctly so that's not really an issue.

 

[MaxRockbin]

Erin said he have 2 rooms, in one of these room sounding meh and another great

I looked at the review again, and you are right. I deleted my comment

 

[phoenixdogfan]

Ah yes my bad, it's $800 extra for meta, since I got the original LS50 at a much lower price there is no discount on the meta and R3.

I am currently playing with the eq as mentioned and the new meta will arrive tomorrow so it's a good opportunity to test original (with/without eq) vs meta. Thanks for the suggestion.

Actually, if you look hard enough, you can finds Metas selling at a discount. I bought my pair for $1200. They were supposedly "scratch and dent" at Crutchfield. When I got them, I might have noticed a small (less than the size of a dime) lighter colored area on one side of the speaker. Might have. Completely invisible when not looking hard for something. Don't think I had to pay sales tax either.

 

[ctrl]

I think it directly causes distortion and it will be measurable. In the form of IMD should be very easy to measure.
However it only happens at higher level which for such driver is not good. At lower level the effect should be very small.

Yep, this is another effect that can occur with coaxial speakers. The excursion of the woofer cone, should actually trigger doppler distortion (sort of) in the tweeter sound radiation, which uses the cone as a waveguide.
However, the audibility should be rather low with small woofer excursion. This could be easily checked experimentally - if I have a lot of time one day...

it doesn’t really give enough credit to how much of the waveguide is static.

Good point, The tangerine waveguide is static and taller than the tweeter.

Yep, you're both right, I hadn't considered that in the simulation. Amir's picture also clearly shows that too.


This should significantly reduce the effects of cone excursion in the highest frequency range (>10kHz, just an estimate).
Interesting, someone should simulate that

 

[MaxRockbin]

This is a correct statement .
You have a lot more freedom in crossover frequencys with two subwoofers in stereo, than with only one subwoofer.
In practice, even with two subwoofers placed at floor level and the kefs on loudspeakerstands, a crossover much higher than 120 Hz is gonna work less good.

People keep suggesting this idea - of stereo subs - but isn't the biggest advantage by far of having two subs the reduction of room modes? Putting them right under your speakers isn't likely to optimize that. Modes will probably impact your sound a lot more than crossing over above 120. If you look at the discussion and comments in this thread about the KEF R3 review, fixing the modes took the speaker from sounding unpleasant or blah, to being outstanding. Modes impact more than lows. Of course, the exact ideal positioning will vary with your room, but how often will it be right under the speakers?

 

[YSC]

Yep, this is another effect that can occur with coaxial speakers. The excursion of the woofer cone, should actually trigger doppler distortion (sort of) in the tweeter sound radiation, which uses the cone as a waveguide.
However, the audibility should be rather low with small woofer excursion. This could be easily checked experimentally - if I have a lot of time one day...



Yep, you're both right, I hadn't considered that in the simulation. Amir's picture also clearly shows that too.
View attachment 146559

This should significantly reduce the effects of cone excursion in the highest frequency range (>10kHz, just an estimate).
Interesting, someone should simulate that

I believe this tangerine waveguide is KEF's solution to the modulation distortion to the cone being used as waveguide, I would imagine only when the woofer excursion is higher than the fixed waveguide and almost reaching it's limit will the HF behavior really show it's effects

 

[Tangband]

People keep suggesting this idea - of stereo subs - but isn't the biggest advantage by far of having two subs the reduction of room modes? Putting them right under your speakers isn't likely to optimize that. Modes will probably impact your sound a lot more than crossing over above 120. If you look at the discussion and comments in this thread about the KEF R3 review, fixing the modes took the speaker from sounding unpleasant or blah, to being outstanding. Modes impact more than lows. Of course, the exact ideal positioning will vary with your room, but how often will it be right under the speakers?

Well, its about swings and roundabouts.
In a difficult room, then two subwoofers crossed much lower at maybe 55 Hz with a steep filter and in mono sometimes can be beneficial. But you then must have mains that can play down to 55 Hz .

I have never, and I repeat, never had a better result with two subs in mono that has been crossed at 80 Hz , than the same subwoofers crossed at 80 Hz in real stereo.

 

[stren]

Simple solution - one SB3000 micro under each LS50 which is rotated 90 degrees, and another one on top. These are passed as high as possible, preferably >200 (if the subs don't HPF above that) which is why you want them above and below the LS50. You'll still need a stand, so maybe just add a 3rd pair of sb3000 micro's as the stand. These can't be crossed as high - maybe keep em to 80Hz now. Then add another two subs elsewhere in the room for room modes

I call it the ls3000 mega tower... Yours for only 1500 + 6*800 USD a pair

 

[YSC]

Simple solution - one SB3000 micro under each LS50 which is rotated 90 degrees, and another one on top. These are passed as high as possible, preferably >200 (if the subs don't HPF above that) which is why you want them above and below the LS50. You'll still need a stand, so maybe just add a 3rd pair of sb3000 micro's as the stand. These can't be crossed as high - maybe keep em to 80Hz now. Then add another two subs elsewhere in the room for room modes

I call it the ls3000 mega tower... Yours for only 1500 + 6*800 USD a pair

Then the ls50’s MDG cabinet can’t take the load… and wait, at that cost and config why don’t I just buy a pair of blade 2 for similar price it takes a lot less plugs to do also

 

[stren]

Then the ls50’s MDG cabinet can’t take the load… and wait, at that cost and config why don’t I just buy a pair of blade 2 for similar price it takes a lot less plugs to do also

Haha well I wasn't quite serious - but even a used pair of blade II's which only uses 6.5" woofers is unlikely to get down to this price. But yes it's pretty silly. I'd suggest a F208 + subs instead if I was serious

 

[Tangband]

Theres a lot of modification threads on the internet with Kef q100 och q150.
Some of them claim better sound than ls50.

One could easily make something that looks like a Kef blade with DIY and the drivers from a Kef q150.
All it takes is eight 6 1/2 inches bass-units for a pair of loudspeakers .
Seas er18rnx is a good candidate.
The price for the bass drivers is about 800 dollars for them all. Four of them would need about 60 liters / channel, bass reflex.

 

[Vahidhm]

What's your xover frequency of the sb2000? Hope its at least 100Hz or more.

I kept it at 80 but anything between 80 to 100 should be fine